A capo (sometimes referred to as a capodastro, capodaster, capotasto or cejilla) is a well-known device used with a stringed instrument having a neck and a set of strings extending along the length of the neck. The capo, when applied to an instrument neck, serves to clamp the strings against a fingerboard and, in particular, between or against one of the number of fret bars disposed along the length of fingerboard. In practice, a capo serves to reduce the effective length of the strings and therefore adjust the pitch; i.e. the pitch is raised as the effective length of a string is shortened. The part of the capo which contacts the strings is usually a resilient pad that prevents damage to the strings from the clamping force.
A twelve-string guitar is a steel-string guitar with twelve strings in six courses, intended to produce a fuller and more ringing tone than a standard six-string guitar. Typically, the strings of the lower four courses are tuned in octaves (a heavy gauge wound string paired with a light gauge wound or non-wound string), with those of the upper two courses tuned in matching pairs (pairs of identical lighter gauge strings). The lower four string pairs are usually arranged such that the first string of each pair, as struck on a downward strum, is the higher octave string; although it is known to reverse this arrangement, such as on a Rickenbacker® electric 12 string guitar. The gap between the strings within each dual-string course is narrow, such that the strings of each course are fretted and plucked as if they were a single string.
As with a six string guitar, a capo can be installed upon a twelve string guitar neck, although it may need to be larger (longer clamping arm) to accommodate the wider neck and extra strings. With a conventional capo the clamping force also generally needs to be greater in order to ensure that the lighter gauge strings make sufficient contact with a fret to result in a clear tone. The consequence of greater clamping pressure, sometimes even right down to the fingerboard, is that it pulls all the strings (predominantly the fatter gauge strings) out of tune and they must be retuned after application or removal of the capo. This presents an undesirable situation when a quick changeover between capo positions is needed during a performance.
To address the problem of clamping differing string gauges in close proximity to one another Paige Musical Products of Michigan, USA produce a capo featuring an offset bar tube that compensates for the smallest of the E, A, D, and G strings on a 12-string guitar. The tubular sleeve sections of this device result in a stepped profile of annular protrusions from the clamp arm where a minimum pressure can be applied until the strings voice clearly, and the controlled tension ensures reduced buzz or string muting. The tubular bar clamp arm is incorporated into a screw threaded clamp arrangement that can be stored behind the nut when not in use.
While the above solution is generally effective it requires time and concentration for a user to apply the capo since, if re-positioning is required further up the neck, the sleeves must be moved to coincide with the string positions (guitar strings typically diverge slightly from one another between the nut and the bridge).